This invention relates to a system or method of verifying the identity of a person by characteristics of his voice.
In identifying a person by the characteristics of his voice, it is a common practice to have a speaker, whose identity is to be verified, utter specific words or clauses and to extract therefrom a characteristic parameter by a certain specified technique and to check said parameter against a prerecorded standard pattern of voice to make a judgement as to whether the voice characteristic is prerecorded based on the magnitude of difference between the two. Generally speaking, a person's voice sometimes changes. This is particularly so when a fairly long time lapses, and a considerable difference is seen between the same person's voice uttered at two different times. Consequently, conventional devices sometimes fail to identify the correct person or incorrectly identify the wrong person.
As a result, it has been devised to extract from the various parameters existing in a person's voice, those having the least possibility of changing with lapse of time and to regard them as the characteristic parameters. While such vocal chord characteristics as information and such sound source as pitch have been considered as appropriate characteristic parameters for voice identification, the latter has hardly been used in practice because it changes drastically with time. Therefore, in most cases only the vocal chord chracteristics, which are liable to change very little, are used. However, it has been discovered that the ability to differentiate or identify voices is greatly improved when sound wave characteristics are used for a short period after recording a standard pattern.